1. Field of the Invention
This invention relates to an improved pump casing for a sheet metal pump and particularly to a pump casing that includes a sheet metal pump body with a reinforced member which has a guide water unit made by casting or injection molding.
2. Description of the Prior Art
Conventional centrifugal pumps are generally made by casting or pressing of sheet metals. The casting method uses cast iron as material which has low stiffness, poor corrosion resistance, and is heavy weight and bulky. It generally has poor durability. It is therefore mainly used for low price pumps. Sheet metal pump made by pressing may have greater mechanical strength, better corrosion resistance such as those made of stainless steel and is light weight and more durable. However sheet meal pump generally has thin casing which is prone to deform under heavy external forces.
It is generally known that the inlet and outlet of the pump casing connecting with outside piping system have to endure great stress resulting from pumping pressure, impeller induced torque and stress, metal strain and stress caused by temperature change and the like. As a result, the pump casing around the inlet and outlet are most likely to deform under pressure. That may cause impeller vibration at high speed and produce excessive friction and noise. To remedy this problem, a number of improvements have been introduced. European Pat. No. EXPO-00442070A1 (Ghiotto) and U.S. Pat. No. 5,310,310 are two of the examples. As shown in FIG. 1, the Ghiotto disclosed a sheet metal pump casing 21 which has a seal ring 23 (or wear ring as also may be called) engaged with the pump casing 21 near the inlet end plate 26 adjacent the inlet 22 located at a front end 25 of the impeller 24 of the centrifugal pump 20.
The seal ring 23 keeps a small gap between the front end of the impeller 24 and the inside wall of the pump casing 21 so that friction may become lower when the impeller 24 rotates at high speed while still having desirable pumping performance. The gap set forth above directly affects pumping efficiency, noise level and durability. Conventional pump has the seal ring fixing to the inlet end plate adjacent the inlet where the deformation is most likely to take place because of the causes given above. Such deformation will cause position shifting of the seal ring and result in greater friction and noise, dropping of pumping efficiency, and shorter durability. Furthermore, the structural strength of conventional sheet metal pumps is general not very strong and consequently reduces its thermo stress strength. Hence the sheet metal pumps made by conventional technique usually work mainly in environments under 150.degree. C.
Moreover, sheet metal pumps made by conventional technique is done by pressing. It is a complex and multiple stages pressing or stamping process to form the tapering cross-section of the volute for containing the impeller. U.S. Pat. No. 5,310,310 discloses a technique that uses multi-stage pressing operations for such purpose. It needs a plurality of different molds. Its production time is longer and the cost is higher. The pressing or stamping operation also tends to produce metal stress concentration that might weaken the mechanical strength of the pump casing.
Conventional metal pump structure also is mostly focused on the reinforcement of the pump casing at the inlet. The pump casing engaging with the motor has often being overlooked. The issues of mechanical strength noise problem and durability at this portion has rarely being addressed. Some may put a back cover 27 (shown in FIG. 1) as a supporting means for the pump casing and the motor. It usually does not have strong enough mechanical strength and may produce heavy vibration at high-speed and great noise and results in poor durability as well.